Pipeline emplacements are often subject to various forces, such as hydrodynamic and hydrostatic forces, for example, which can manifest in the displacement of the pipeline from its originally installed position. Consequential pipeline rupture can have adverse environmental and financial repercussions.
Responsible pipeline companies and contractors are committed to installations whose designs provide for a high margin of design tolerance over and above any purely structural requirement for pipeline weighting. This abundance of caution is intended to offset the catastrophic potential attached to taking unwarranted risks that might lead to displacement and consequential pipeline damage, including service interruption, and environmental damage.
To that end, the traditional, and still predominating practice in the industry, entails weighting the pipeline with massive concrete weights. Earlier designs include clamp-on-weights of various descriptions, as well as the more typical large pre-cast concrete arch structures that are arranged in bridging relation over top of the pipeline. These latter mentioned designs are currently the most widely-used. At the same time, they are expensive to fabricate, transport, entail labour intensive installation practices, and generally require increased trench depth and width dimensions in order that their installation can be properly accommodated. Current thinking in the relevant art is that even though these weights are very expensive, the protection they afford in terms of securely anchoring a pipeline more than offsets their associated materials and installation costs, once consideration is given to the repair and clean-up costs that could ensue in the event of any breech, or rupture, such as might otherwise be attributable to shifting of an unweighted, or improperly weighted pipeline emplacement.
Although such weights might be used in any number of situations, they appear most commonly in in-ground installations. In subterranean pipeline emplacements, the problem of pipeline leakage is, (from the point of view of precisely locating the problem, rapidly containing spillage and repairing any damage), most acute. Underground emplacements are also susceptible to hydrostatic forces, which can cause the pipeline to be displaced from the position it occupied when originally installed, possibly leading to such a rupture or breech. With this in mind, it will be readily appreciated that subterranean emplacements are quantitatively demanding, if not qualitatively exceptional from the point of view of pipeline weighting in such emplacements.
One proposed alternative for dealing with the problem of maintaining the positioning of a pipeline within a subterranean emplacement is disclosed in U.S. Pat. No. 3,170,663--Fite. This patent discloses an anchoring device for a pipeline, which incorporates an arcuate collar that is secured in straddling relation about the upper exterior surface of the pipeline. The collar is held in tensioned relation against that surface by a laterally spaced apart pair of anchoring rods having spiral flights thereon that extend beyond the under surface of the pipeline are adapted to positively engage the underlying soil substrate on either side thereof.
Another proposal entails the use, in muskeg environments, of simple two-dimensional sheets of a fabric that are intended to be deployed in a pipeline trench, overlaying the installed pipeline. Backfill is then layered over the fabric in the hope that the collected "unit weight" of the resulting overburden will be sufficient to counter any buoyant forces that local ground water might exert on the pipeline. Resort to this approach has been entertained only when alternatives are simply not available, (i.e. in remote muskeg areas). Moreover, there is a risk that ground water flows will displace some of the "unit weight" of the "disturbed" backfill from above the pipeline. This would be a particular problem in areas where ground surface contours or the grading of the emplacement or a non-level transit of the pipeline, might result in either or both surface and ground water flows that could be channelled within the fabric, almost in the manner of an artificial canal.
There remains a need in the art to reconcile the necessity of anchoring pipelines for the purpose of avoiding or reducing the impact of some of the problems set out above, with the apparently antithetical desire for any reduction in the high costs heretofore associated with the practices that the industry has been willing to embrace.